Methods and apparatus for embedding watermarks

ABSTRACT

Methods and apparatus for embedding a watermark are disclosed. An example method disclosed herein to embed a watermark in a compressed data stream comprises obtaining a set of transform coefficients included in the compressed data stream, the set of transform coefficients having a respective first set of mantissa codes and a respective set of exponents, the first set of mantissa codes associated with a respective set of mantissa step sizes, identifying a first transform coefficient from the set of transform coefficients having a smallest magnitude among the set of transform coefficients, determining a second set of mantissa codes based on the first transform coefficient and the set of step sizes, and replacing the first set of mantissa codes included in the compressed data stream with the second set of mantissa codes to embed the watermark without uncompressing the compressed data stream.

RELATED APPLICATIONS

This patent arises from a continuation of U.S. application Ser. No.13/283,271 filed on Oct. 27, 2011, which is a continuation of U.S.application Ser. No. 12/613,334 filed on Nov. 5, 2009 (now U.S. Pat. No.8,085,975), which is a continuation of U.S. application Ser. No.12/269,733 filed on Nov. 12, 2008 (now U.S. Pat. No. 7,643,652), whichis a continuation of U.S. application Ser. No. 11/298,040 filed on Dec.9, 2005 (now U.S. Pat. No. 7,460,684), which is a continuation of PCTApplication Serial No. PCT/US2004/018953 filed Jun. 14, 2004, whichclaims the benefit of the filing date of U.S. Provisional ApplicationNo. 60/478,626, filed Jun. 13, 2003, and the benefit of U.S. ProvisionalApplication No. 60/571,258, filed May 14, 2004, the disclosures of whichare hereby incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to media measurements, and moreparticularly, to methods and apparatus for embedding watermarks in acompressed digital data stream.

BACKGROUND

In modern television or radio broadcast stations, compressed digitaldata streams are typically used to carry video and/or audio data fortransmission. For example, the Advanced Television Systems Committee(ATSC) standard for digital television (DTV) broadcasts in the UnitedStates adopted Moving Picture Experts Group (MPEG) standards (e.g.,MPEG-1, MPEG-2, MPEG-3, MPEG-4, etc.) for carrying video content andDigital Audio Compression standards (e.g., AC-3, which is also known asDolby Digital®) for carrying audio content (i.e., ATSC Standard: DigitalAudio Compression (AC-3), Revision A, August 2001). The AC-3 compressionstandard is based on a perceptual digital audio coding technique thatreduces the amount of data needed to reproduce the original audio signalwhile minimizing perceptible distortion. In particular, the AC-3compression standard recognizes that the human ear is unable to perceivechanges in spectral energy at particular spectral frequencies that aresmaller than the masking energy at those spectral frequencies. Themasking energy is a characteristic of an audio segment dependent on thetonality and noise-like characteristic of the audio segment. Differentknown psycho-acoustic models may be used to determine the masking energyat a particular spectral frequency. Further, the AC-3 compressionstandard provides a multi-channel digital audio format (e.g., 5.1channels format) for digital television (DTV), high definitiontelevision (HDTV), digital versatile discs (DVDs), digital cable, andsatellite transmissions that enables the broadcast of special soundeffects (e.g., surround sound).

Existing television or radio broadcast stations employ watermarkingtechniques to embed watermarks within video and/or audio data streamscompressed in accordance with compression standards such as the AC-3compression standard and the MPEG Advanced Audio Coding (AAC)compression standard. Typically, watermarks are digital data thatuniquely identify broadcasters and/or programs. Watermarks are typicallyextracted using a decoding operation at one or more reception sites(e.g., households or other media consumption sites) and, thus, may beused to assess the viewing behaviors of individual households and/orgroups of households to produce ratings information.

However, many existing watermarking techniques are designed for use withanalog broadcast systems. In particular, existing watermarkingtechniques convert analog program data to an uncompressed digital datastream, insert watermark data in the uncompressed digital data stream,and convert the watermarked data stream to an analog format prior totransmission. In the ongoing transition towards an all-digital broadcastenvironment in which compressed video and audio streams are transmittedby broadcast networks to local affiliates, watermark data may need to beembedded or inserted directly in a compressed digital data stream.Existing watermarking techniques may decompress the compressed digitaldata stream into time-domain samples, insert the watermark data into thetime-domain samples, and recompress the watermarked time-domain samplesinto a watermarked compressed digital data stream. Suchdecompression/compression may cause degradation in the quality of themedia content in the compressed digital data stream. Further, existingdecompression/compression techniques require additional equipment andcause delay of the audio component of a broadcast in a manner that, insome cases, may be unacceptable. Moreover, the methods employed by localbroadcasting affiliates to receive compressed digital data streams fromtheir parent networks and to insert local content through sophisticatedsplicing equipment prevent conversion of a compressed digital datastream to a time-domain (uncompressed) signal prior to recompression ofthe digital data streams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representation of an example media monitoringsystem.

FIG. 2 is a block diagram representation of an example watermarkembedding system.

FIG. 3 is a block diagram representation of an example uncompresseddigital data stream associated with the example watermark embeddingsystem of FIG. 2.

FIG. 4 is a block diagram representation of an example embedding devicethat may be used to implement the example watermark embedding system ofFIG. 2.

FIG. 5 depicts an example compressed digital data stream associated withthe example embedding device of FIG. 4.

FIG. 6 depicts an example quantization look-up table that may be used toimplement the example watermark embedding system of FIG. 2.

FIG. 7 depicts another example uncompressed digital data stream that maybe compressed and then processed using the example watermark embeddingsystem of FIG. 2.

FIG. 8 depicts an example compressed digital data stream associated withthe example uncompressed digital data stream of FIG. 7.

FIG. 9 depicts one manner in which the example watermark embeddingsystem of FIG. 2 may be configured to embed watermarks.

FIG. 10 depicts one manner in which the modification process of FIG. 9may be implemented.

FIG. 11 depicts one manner in which a data frame may be processed.

FIG. 12 depicts one manner in which a watermark may be embedded in acompressed digital data stream.

FIG. 13 depicts an example code frequency index table that may be usedto implement the example watermark embedding system of FIG. 2.

FIG. 14 is a block diagram representation of an example processor systemthat may be used to implement the example watermark embedding system ofFIG. 2.

DETAILED DESCRIPTION

In general, methods and apparatus for embedding watermarks in compresseddigital data streams are disclosed herein. The methods and apparatusdisclosed herein may be used to embed watermarks in compressed digitaldata streams without prior decompression of the compressed digital datastreams. As a result, the methods and apparatus disclosed hereineliminate the need to subject compressed digital data streams tomultiple decompression/compression cycles, which are typicallyunacceptable to, for example, affiliates of television broadcastnetworks because multiple decompression/compression cycles maysignificantly degrade the quality of media content in the compresseddigital data streams.

Prior to broadcast, for example, the methods and apparatus disclosedherein may be used to unpack the modified discrete cosine transform(MDCT) coefficient sets associated with a compressed digital data streamformatted according to a digital audio compression standard such as theAC-3 compression standard. The mantissas of the unpacked MDCTcoefficient sets may be modified to embed watermarks that imperceptiblyaugment the compressed digital data stream. Upon receipt of thecompressed digital data stream, a receiving device (e.g., a set toptelevision metering device at a media consumption site) may extract theembedded watermark information from an uncompressed analog output suchas, for example, output emanating from speakers of a television set. Theextracted watermark information may be used to identify the mediasources and/or programs (e.g., broadcast stations) associated with mediacurrently being consumed (e.g., viewed, listened to, etc.) at a mediaconsumption site. In turn, the source and program identificationinformation may be used in known manners to generate ratings informationand/or any other information that may be used to assess the viewingbehaviors associated with individual households and/or groups ofhouseholds.

Referring to FIG. 1, an example broadcast system 100 including a serviceprovider 110, a television 120, a remote control device 125, and areceiving device 130 is metered using an audience measurement system.The components of the broadcast system 100 may be coupled in anywell-known manner. For example, the television 120 is positioned in aviewing area 150 located within a household occupied by one or morepeople, referred to as household members 160, some or all of whom haveagreed to participate in an audience measurement research study. Thereceiving device 130 may be a set top box (STB), a video cassetterecorder, a digital video recorder, a personal video recorder, apersonal computer, a digital video disc player, etc. coupled to thetelevision 120. The viewing area 150 includes the area in which thetelevision 120 is located and from which the television 120 may beviewed by the one or more household members 160 located in the viewingarea 150.

In the illustrated example, a metering device 140 is configured toidentify viewing information based on video/audio output signalsconveyed from the receiving device 130 to the television 120. Themetering device 140 provides this viewing information as well as othertuning and/or demographic data via a network 170 to a data collectionfacility 180. The network 170 may be implemented using any desiredcombination of hardwired and wireless communication links, including forexample, the Internet, an Ethernet connection, a digital subscriber line(DSL), a telephone line, a cellular telephone system, a coaxial cable,etc. The data collection facility 180 may be configured to processand/or store data received from the metering device 140 to produceratings information.

The service provider 110 may be implemented by any service provider suchas, for example, a cable television service provider 112, a radiofrequency (RF) television service provider 114, and/or a satellitetelevision service provider 116. The television 120 receives a pluralityof television signals transmitted via a plurality of channels by theservice provider 110 and may be adapted to process and displaytelevision signals provided in any format such as a National TelevisionStandards Committee (NTSC) television signal format, a high definitiontelevision (HDTV) signal format, an Advanced Television SystemsCommittee (ATSC) television signal format, a phase alternation line(PAL) television signal format, a digital video broadcasting (DVB)television signal format, an Association of Radio Industries andBusinesses (ARIB) television signal format, etc.

The user-operated remote control device 125 allows a user (e.g., thehousehold member 160) to cause the television 120 to tune to and receivesignals transmitted on a desired channel, and to cause the television120 to process and present or deliver the programming or media contentcontained in the signals transmitted on the desired channel. Theprocessing performed by the television 120 may include, for example,extracting a video and/or an audio component delivered via the receivedsignal, causing the video component to be displayed on a screen/displayassociated with the television 120, and causing the audio component tobe emitted by speakers associated with the television 120. Theprogramming content contained in the television signal may include, forexample, a television program, a movie, an advertisement, a video game,a web page, a still image, and/or a preview of other programming contentthat is currently offered or will be offered in the future by theservice provider 110.

While the components shown in FIG. 1 are depicted as separate structureswithin the broadcast system 100, the functions performed by some ofthese structures may be integrated within a single unit or may beimplemented using two or more separate components. For example, althoughthe television 120 and the receiving device 130 are depicted as separatestructures, the television 120 and the receiving device 130 may beintegrated into a single unit (e.g., an integrated digital televisionset). In another example, the television 120, the receiving device 130,and/or the metering device 140 may be integrated into a single unit.

To assess the viewing behaviors of individual household members 160and/or groups of households, a watermark embedding system (e.g., thewatermark embedding system 200 of FIG. 2) may encode watermarks thatuniquely identify broadcasters and/or programs in the broadcast signalsfrom the service providers 110. The watermark embedding system may beimplemented at the service provider 110 so that each of the plurality ofmedia signals (e.g., television signals) transmitted by the serviceprovider 110 includes one or more watermarks. Based on selections by thehousehold members 160, the receiving device 130 may tune to and receivemedia signals transmitted on a desired channel and cause the television120 to process and present the programming content contained in thesignals transmitted on the desired channel. The metering device 140 mayidentify watermark information based on video/audio output signalsconveyed from the receiving device 130 to the television 120.Accordingly, the metering device 140 may provide this watermarkinformation as well as other tuning and/or demographic data to the datacollection facility 180 via the network 170.

In FIG. 2, an example watermark embedding system 200 includes anembedding device 210 and a watermark source 220. The embedding device210 is configured to insert watermark information 230 from the watermarksource 220 into a compressed digital data stream 240. The compresseddigital data stream 240 may be compressed according to an audiocompression standard such as the AC-3 compression standard and/or theMPEG-AAC compression standard, either of which may be used to processblocks of an audio signal using a predetermined number of digitizedsamples from each block. The source of the compressed digital datastream 240 (not shown) may be sampled at a rate of, for example, 48kilohertz (kHz) to form audio blocks as described below.

Typically, audio compression techniques such as those based on the AC-3compression standard use overlapped audio blocks and the MDCT algorithmto convert an audio signal into a compressed digital data stream (e.g.,the compressed digital data stream 240 of FIG. 2). Two different blocksizes (i.e., short and long blocks) may be used depending on the dynamiccharacteristics of the sampled audio signal. For example, AC-3 shortblocks may be used to minimize pre-echo for transient segments of theaudio signal and AC-3 long blocks may be used to achieve highcompression gain for non-transient segments of the audio signal. Inaccordance with the AC-3 compression standard an AC-3 long blockcorresponds to a block of 512 time-domain audio samples, whereas an AC-3short block corresponds to 256 time-domain audio samples. Based on theoverlapping structure of the MDCT algorithm used in the AC-3 compressionstandard, in the case of the AC-3 long block, the 512 time-domainsamples are obtained by concatenating a preceding (old) block of 256time-domain samples and a current (new) block of 256 time-domain samplesto create an audio block of 512 time-domain samples. The AC-3 long blockis then transformed using the MDCT algorithm to generate 256 transformcoefficients. In accordance with the same standard, an AC-3 short blockis similarly obtained from a pair of consecutive time-domain sampleblocks of audio. The AC-3 short block is then transformed using the MDCTalgorithm to generate 128 transform coefficients. The 128 transformcoefficients corresponding to two adjacent short blocks are theninterleaved to generate a set of 256 transform coefficients. Thus,processing of either AC-3 long or AC-3 short blocks results in the samenumber of MDCT coefficients. In accordance with the MPEG-AAC compressionstandard as another example, a short block contains 128 samples and along block contains 1024 samples.

In the example of FIG. 3, an uncompressed digital data stream 300includes a plurality of 256-sample time-domain audio blocks 310,generally shown as A0, A1, A2, A3, A4, and A5. The MDCT algorithmprocesses the audio blocks 310 to generate MDCT coefficient sets 320,shown by way of example as MA0, MA1, MA2, MA3, MA4, and MA5 (where MA5is not shown). For example, the MDCT algorithm may process the audioblocks A0 and A1 to generate the MDCT coefficient set MA0. The audioblocks A0 and A1 are concatenated to generate a 512-sample audio block(e.g., an AC-3 long block) that is MDCT transformed using the MDCTalgorithm to generate the MDCT coefficient set MA0 which includes 256MDCT coefficients. Similarly, the audio blocks A1 and A2 may beprocessed to generate the MDCT coefficient set MA1. Thus, the audioblock A1 is an overlapping audio block because it is used to generateboth MDCT coefficient sets MA0 and MA1. In a similar manner, the MDCTalgorithm is used to transform the audio blocks A2 and A3 to generatethe MDCT coefficient set MA2, the audio blocks A3 and A4 to generate theMDCT coefficient set MA3, the audio blocks A4 and A5 to generate theMDCT coefficient set MA4, etc. Thus, the audio block A2 is anoverlapping audio block used to generate the MDCT coefficient sets MA1and MA2, the audio block A3 is an overlapping audio block used togenerate the MDCT coefficient sets MA2 and MA3, the audio block A4 is anoverlapping audio block used to generate the MDCT coefficient sets MA3and MA4, etc. Together, the MDCT coefficient sets 320 form thecompressed digital data stream 240.

As described in detail below, the embedding device 210 of FIG. 2 mayembed or insert the watermark information or watermark 230 from thewatermark source 220 into the compressed digital data stream 240. Thewatermark 230 may be used, for example, to uniquely identifybroadcasters and/or programs so that media consumption information(e.g., viewing information) and/or ratings information may be produced.Accordingly, the embedding device 210 produces a watermarked compresseddigital data stream 250 for transmission.

In the example of FIG. 4, the embedding device 210 includes anidentifying unit 410, an unpacking unit 420, a modification unit 430,and a repacking unit 440. While the operation of the embedding device210 is described below in accordance with the AC-3 compression standard,the embedding device 210 may be implemented to operate with additionalor other compression standards such as, for example, the MPEG-AACcompression standard. The operation of the embedding device 210 isdescribed in greater detail in connection with FIG. 5.

To begin, the identifying unit 410 is configured to identify one or moreframes 510 associated with the compressed digital data stream 240, aportion of which is shown by way of example as Frame A and Frame B inFIG. 5. As mentioned previously, the compressed digital data stream 240may be a digital data stream compressed in accordance with the AC-3standard (hereinafter “AC-3 data stream”). While the AC-3 data stream240 may include multiple channels, for purposes of clarity, thefollowing example describes the AC-3 data stream 240 as including onlyone channel. In the AC-3 data stream 240, each of the frames 510includes a plurality of MDCT coefficient sets 520. In accordance withthe AC-3 compression standard, for example, each of the frames 510includes six MDCT coefficient sets (i.e., six “audblk”). For example,Frame A includes the MDCT coefficient sets MA0, MA1, MA2, MA3, MA4 andMA5 and Frame B includes the MDCT coefficient sets MB0, MB1, MB2, MB3,MB4 and MB5.

The identifying unit 410 is also configured to identify headerinformation associated with each of the frames 510, such as, forexample, the number of channels associated with the AC-3 data stream240. While the example AC-3 data stream 240 includes only one channel asnoted above, an example compressed digital data stream having multiplechannels is described below in connection with FIGS. 7 and 8.

Returning to FIG. 5, the unpacking unit 420 is configured to unpack theMDCT coefficient sets 520 to determine compression information such as,for example, the parameters of the original compression process (i.e.,the manner in which an audio compression technique compressed an audiosignal or audio data to form the compressed digital data stream 240).For example, the unpacking unit 420 may determine how many bits are usedto represent each of the MDCT coefficients within the MDCT coefficientsets 520. Additionally, compression parameters may include informationthat limits the extent to which the AC-3 data stream 240 may be modifiedto ensure that the media content conveyed via the AC-3 data stream 240is of a sufficiently high quality level. The embedding device 210subsequently uses the compression information identified by theunpacking unit 420 to embed/insert the desired watermark information 230into the AC-3 data stream 240 thereby ensuring that the watermarkinsertion is performed in a manner consistent with the compressioninformation supplied in the signal.

As described in detail in the AC-3 compression standard, the compressioninformation also includes a mantissa and an exponent associated witheach MDCT coefficient. The AC-3 compression standard employs techniquesto reduce the number of bits used to represent each MDCT coefficient.Psycho-acoustic masking is one factor that may be utilized by thesetechniques. For example, the presence of audio energy E_(k) either at aparticular frequency k (e.g., a tone) or spread across a band offrequencies proximate to the particular frequency k (e.g., a noise-likecharacteristic) creates a masking effect. That is, the human ear isunable to perceive a change in energy in a spectral region either at afrequency k or spread across the band of frequencies proximate to thefrequency k if that change is less than a given energy threshold ΔE_(k).Because of this characteristic of the human ear, an MDCT coefficientm_(k) associated with the frequency k may be quantized with a step sizerelated to ΔE_(k) without risk of causing any humanly perceptiblechanges to the audio content. For the AC-3 data stream 240, each MDCTcoefficient m_(k) is represented as a mantissa M_(k) and an exponentX_(k) such that m_(k)=M_(k)·2^(−X) _(k). The number of bits used torepresent the mantissa M_(k) of each MDCT coefficient of the MDCTcoefficient sets 520 may be determined based on known quantizationlook-up tables published in the AC-3 compression standard (e.g., thequantization look-up table 600 of FIG. 6). In the example of FIG. 6, thequantization look-up table 600 provides mantissa codes or bit patternsand corresponding mantissa values for MDCT coefficients represented by afour-bit number. As described in detail below, the mantissa M_(k) may bechanged (e.g., augmented) to represent a modified value of an MDCTcoefficient to embed a watermark in the AC-3 data stream 240.

Returning to FIG. 5, the modification unit 430 is configured to performan inverse transform of each of the MDCT coefficient sets 520 togenerate time-domain audio blocks 530, shown by way of example as TA0′,TA3″, TA4′, TA4″, TA5′, TA5″, TB0′, TB0″, TB1′, TB1″, and TB5′ (TA0″through TA3′ and TB2′ through TB4″ are not shown). The modification unit430 performs inverse transform operations to generate sets of previous(old) time-domain audio blocks (which are represented as prime blocks)and sets of current (new) time-domain audio blocks (which arerepresented as double-prime blocks) associated with the 256-sampletime-domain audio blocks that were concatenated to form the MDCTcoefficient sets 520 of the AC-3 data stream 240. For example, themodification unit 430 performs an inverse transform on the MDCTcoefficient set MA5 to generate time-domain blocks TA4″ and TA5′, theMDCT coefficient set MB0 to generate TA5″ and TB0′, the MDCT coefficientset MB1 to generate TB0″ and TB1′, etc. In this manner, the modificationunit 430 generates reconstructed time-domain audio blocks 540, whichprovide a reconstruction of the original time-domain audio blocks thatwere compressed to form the AC-3 data stream 240. To generate thereconstructed time-domain audio blocks 540, the modification unit 430may add time-domain audio blocks based on, for example, the knownPrincen-Bradley time domain alias cancellation (TDAC) technique asdescribed in Princen et al., Analysis/Synthesis Filter Bank Design Basedon Time Domain Aliasing Cancellation, Institute of Electrical andElectronics Engineers (IEEE) Transactions on Acoustics, Speech andSignal Processing, Vol. ASSP-35, No. 5, pp. 1153-1161 (1996). Forexample, the modification unit 430 may reconstruct the time-domain audioblock TA5 (i.e., TA5R) by adding the prime time-domain audio block TA5′and the double-prime time-domain audio block TA5″ using thePrincen-Bradley TDAC technique. Likewise, the modification unit 430 mayreconstruct the time-domain audio block TB0 (i.e., TB0R) by adding theprime audio block TB0′ and the double-prime audio block TB0″ using thePrincen-Bradley TDAC technique. In this manner, the original time-domainaudio blocks used to form the AC-3 data stream 240 are reconstructed toenable the watermark 230 to be embedded or inserted directly into theAC-3 data stream 240.

The modification unit 430 is also configured to insert the watermark 230into the reconstructed time-domain audio blocks 540 to generatewatermarked time-domain audio blocks 550, shown by way of example asTA0W, TA4W, TA5W, TB0W, TB1W and TB5W (blocks TA1W, TA2W, TA3W, TB2W,TB3W and TB4W are not shown). To insert the watermark 230, themodification unit 430 generates a modifiable time-domain audio block byconcatenating two adjacent reconstructed time-domain audio blocks tocreate a 512-sample audio block. For example, the modification unit 430may concatenate the reconstructed time-domain audio blocks TA5R and TB0R(each being a 256-sample audio block) to form a 512-sample audio block.The modification unit 430 may then insert the watermark 230 into the512-sample audio block formed by the reconstructed time-domain audioblocks TA5R and TB0R to generate the watermarked time-domain audioblocks TA5W and TBOW. Encoding processes such as those described in U.S.Pat. Nos. 6,272,176, 6,504,870, and 6,621,881 may be used to insert thewatermark 230 into the reconstructed time-domain audio blocks 540. Thedisclosures of U.S. Pat. Nos. 6,272,176, 6,504,870, and 6,621,881 arehereby incorporated by reference herein in their entireties.

In the example encoding methods and apparatus described in U.S. Pat.Nos. 6,272,176, 6,504,870, and 6,621,881, watermarks may be insertedinto a 512-sample audio block. For example, each 512-sample audio blockcarries one bit of embedded or inserted data of the watermark 230. Inparticular, spectral frequency components with indices f₁ and f₂ may bemodified or augmented to insert data bits associated with the watermark230. To insert a binary “1,” for example, a power at the first spectralfrequency associated with the index f₁ may be increased or augmented tobe a spectral power maximum within a frequency neighborhood (e.g., afrequency neighborhood defined by the indices f₁−2, f₁−1, f₁, f₁+1, andf₁+2). At the same time, the power at the second spectral frequencyassociated with the index f₂ is attenuated or augmented to be a spectralpower minimum within a frequency neighborhood (e.g., a frequencyneighborhood defined by the indices f₂−2, f₂−1, f₂, f₂+1, and f₂+2).Conversely, to insert a binary “0,” the power at the first spectralfrequency associated with the index f₁ is attenuated to be a localspectral power minimum while the power at the second spectral frequencyassociated with the index f₂ is increased to a local spectral powermaximum.

Returning to FIG. 5, based on the watermarked time-domain audio blocks550, the modification unit 430 generates watermarked MDCT coefficientsets 560, shown by way of example as MA0W, MA4W, MA5W, MB0W and MB5W(blocks MA1W, MA2W, MA3W, MB1W, MB2W, MB3W and MB4W are not shown).Following the example described above, the modification unit 430generates the watermarked MDCT coefficient set MA5W based on thewatermarked time-domain audio blocks TA5W and TB0W. Specifically, themodification unit 430 concatenates the watermarked time-domain audioblocks TA5W and TB0W to form a 512-sample audio block and converts the512-sample audio block into the watermarked MDCT coefficient set MA5Wwhich, as described in greater detail below, may be used to modify theoriginal MDCT coefficient set MA5.

The difference between the MDCT coefficient sets 520 and the watermarkedMDCT coefficient sets 560 represents a change in the AC-3 data stream240 as a result of embedding or inserting the watermark 230. Asdescribed in connection with FIG. 6, for example, the modification unit430 may modify the mantissa values in the MDCT coefficient set MA5 basedon the differences between the coefficients in the correspondingwatermarked MDCT coefficient set MA5W and the coefficients in theoriginal MDCT coefficient set MA5. Quantization look-up tables (e.g.,the look-up table 600 of FIG. 6) may be used to determine new mantissavalues associated with the MDCT coefficients of the watermarked MDCTcoefficient sets 560 to replace the old mantissa values associated withthe MDCT coefficients of the MDCT coefficient sets 520. Thus, the newmantissa values represent the change in or augmentation of the AC-3 datastream 240 as a result of embedding or inserting the watermark 230. Itis important to note that, in this example implementation, the exponentsof the MDCT coefficients are not changed. Changing the exponents mightrequire that the underlying compressed signal representation berecomputed, thereby requiring the compressed signal to undergo a truedecompression/compression cycle. If a modification of only the mantissais insufficient to fully account for the difference between awatermarked and an original MDCT coefficient, the affected MDCT mantissais set to a maximum or minimum value, as appropriate. The redundancyincluded in the watermarking process allows the correct watermark to bedecoded in the presence of such an encoding restriction.

Turning to FIG. 6, the example quantization look-up table 600 includesmantissa codes and mantissa values for a fifteen-level quantization ofan example mantissa M_(k) in the range of −0.9333 to +0.9333. While theexample quantization look-up table 600 provides mantissa informationassociated with MDCT coefficients that are represented using four bits,the AC-3 compression standard provides quantization look-up tablesassociated with other suitable numbers of bits per MDCT coefficient. Toillustrate one manner in which the modification unit 430 may modify aparticular MDCT coefficient m_(k) with a mantissa M_(k) contained in theMDCT coefficient set MA5, assume the original mantissa value is −0.2666(i.e., − 4/15). Using the quantization look-up table 600, the mantissacode corresponding to the particular MDCT coefficient m_(k) in the MDCTcoefficient set MA5 is determined to be 0101. The watermarked MDCTcoefficient set MA5W includes a watermarked MDCT coefficient wm_(k) witha mantissa value WM_(k). Further, assume the new mantissa value of thecorresponding watermarked MDCT coefficient wm_(k) of the watermarkedMDCT coefficient set MA5W is −0.4300, which lies between the mantissacodes of 0011 and 0100. In other words, the watermark 230, in thisexample, results in a difference of −0.1667 between the originalmantissa value of −0.2666 and the watermarked mantissa value of −0.4300.

To embed or insert the watermark 230 in the AC-3 data stream 240, themodification unit 430 may use the watermarked MDCT coefficient set MA5Wto modify or augment the MDCT coefficients in the MDCT coefficient setMA5. Continuing with above example, either mantissa code 0011 ormantissa code 0100 may replace the mantissa code 0101 associated withthe MDCT coefficient m_(k) because the watermarked mantissa WM_(k)associated with the corresponding watermarked MDCT coefficient wm_(k)lies between the mantissa codes of 0011 and 0100 (because the mantissavalue corresponding to the watermarked MDCT coefficient wm_(k) is−0.4300). The mantissa value corresponding to the mantissa code 0011 is−0.5333 (i.e., −8/15) and the mantissa value corresponding to themantissa code 0100 is −0.4 (i.e., −6/15). In this example, themodification unit 430 selects the mantissa code 0100 instead of themantissa code 0011 to replace the original mantissa code 0101 associatedwith the MDCT coefficient m_(k) because the mantissa value −0.4corresponding to the mantissa code 0100 is closest to the desiredwatermark mantissa value −0.4300. As a result, the new mantissa bitpattern of 0100, which corresponds to the watermarked mantissa WM_(k) ofthe watermarked MDCT coefficient wm_(k), replaces the original mantissabit pattern of 0101. Likewise, each of the MDCT coefficients in the MDCTcoefficient set MA5 may be modified in the manner described above. If awatermarked mantissa value is outside the quantization range of mantissavalues (i.e., greater than 0.9333 or less than −0.9333), either thepositive limit of 1110 or the negative limit of 0000 is selected as thenew mantissa code, as appropriate. Additionally, and as discussed above,while the mantissa codes associated with each MDCT coefficient of anMDCT coefficient set may be modified as described above, the exponentsassociated with the MDCT coefficients remain unchanged.

The repacking unit 440 is configured to repack the watermarked MDCTcoefficient sets 560 associated with each frame of the AC-3 data stream240 for transmission. In particular, the repacking unit 440 identifiesthe position of each MDCT coefficient set within a frame of the AC-3data stream 240 so that the corresponding watermarked MDCT coefficientset can be used to modify the MDCT coefficient set. To rebuild awatermarked version of Frame A, for example, the repacking unit 440 mayidentify the position of and modify the MDCT coefficient sets MA0 to MA5based on the corresponding watermarked MDCT coefficient sets MA0W toMA5W in the corresponding identified positions. Using the unpacking,modifying, and repacking processes described herein, the AC-3 datastream 240 remains a compressed digital data stream while the watermark230 is embedded or inserted in the AC-3 data stream 240. As a result,the embedding device 210 inserts the watermark 230 into the AC-3 datastream 240 without additional decompression/compression cycles that maydegrade the quality of the media content in the AC-3 data stream 240.

For simplicity, the AC-3 data stream 240 is described in connection withFIG. 5 to include a single channel. However, the methods and apparatusdisclosed herein may be applied to compressed digital data streamshaving audio blocks associated with multiple channels, such as 5.1channels (i.e., five full-bandwidth channels), as described below. Inthe example of FIG. 7, an uncompressed digital data stream 700 mayinclude a plurality of audio block sets 710. Each of the audio blocksets 710 may include audio blocks associated with multiple channels 720and 730 including, for example, a front left channel, a front rightchannel, a center channel, a surround left channel, a surround rightchannel, and a low-frequency effect (LFE) channel (e.g., a sub-wooferchannel). For example, the audio block set AUD0 includes an audio blockA0L associated with the front left channel, an audio block A0Rassociated with the front right channel, an audio block A0C associatedwith the center channel, an audio block A0SL associated with thesurround left channel, an audio block A0SR associated with the surroundright channel, and an audio block A0LFE associated with the LFE channel.Similarly, the audio block set AUD1 includes an audio block A1Lassociated with the front left channel, an audio block A1R associatedwith the front right channel, an audio block A1C associated with thecenter channel, an audio block A1SL associated with the surround leftchannel, an audio block A1SR associated with the surround right channel,and an audio block A1LFE associated with the LFE channel.

Each of the audio blocks associated with a particular channel in theaudio block sets 710 may be processed in a manner similar to thatdescribed above in connection with FIGS. 5 and 6. For example, the audioblocks associated with the center channel 810 of FIG. 8, shown by way ofexample as A0C, A1C, A2C, and A3C, may be transformed to generate theMDCT coefficient sets 820 associated with a compressed digital datastream 800. As noted above, each of the MDCT coefficient sets 820 may bederived from a 512-sample audio block formed by concatenating apreceding (old) 256-sample audio block and a current (new) 256-sampleaudio block. The MDCT algorithm may then process the time-domain audioblocks 810 (e.g., A0C through A5C) to generate the MDCT coefficient sets(e.g., M0C through M5C).

Based on the MDCT coefficient sets 820 of the compressed digital datastream 800, the identifying unit 410 identifies a plurality of frames(not shown) and header information associated with each of the frames asdescribed above. The header information includes compression informationassociated with the compressed digital data stream 800. For each of theframes, the unpacking unit 420 unpacks the MDCT coefficient sets 820 todetermine the compression information associated with the MDCTcoefficient sets 820. For example, the unpacking unit 420 may identifythe number of bits used by the original compression process to representthe mantissa of each MDCT coefficient in each of the MDCT coefficientsets 820. Such compression information may be used to embed thewatermark 230 as described above in connection with FIG. 6. Themodification unit 430 then generates inverse transformed time-domainaudio blocks 830, shown by way of example as TA0C″, TA1C′, TA1C″, TA2C′,TA2C″, and TA3C′. The time-domain audio blocks 830 include a set ofprevious (old) time-domain audio blocks (which are represented as primeblocks) and a set of current (new) time-domain audio blocks (which arerepresented as double-prime blocks). By adding the corresponding primeblocks and double-prime blocks based on, for example, thePrincen-Bradley TDAC technique, original time-domain audio blockscompressed to form the AC-3 digital data stream 800 may be reconstructed(i.e., the reconstructed time-domain audio blocks 840). For example, themodification unit 430 may add the time-domain audio blocks TA1C′ andTA1C″ to reconstruct the time-domain audio block TA1C (i.e., TA1CR).Likewise, the modification unit 430 may add the time-domain audio blocksTA2C′ and TA2C″ to reconstruct the time-domain audio block TA2C (i.e.,TA2CR).

To insert the watermark 230 from the watermark source 220, themodification unit 430 concatenates two adjacent reconstructedtime-domain audio blocks to create a 512-sample audio block (i.e., amodifiable time-domain audio block). For example, the modification unit430 may concatenate the reconstructed time-domain audio blocks TA1CR andTA2CR, each of which is a 256-sample short block, to form a 512-sampleaudio block. The modification unit 430 then inserts the watermark 230into the 512-sample audio block formed by the reconstructed time-domainaudio blocks TA1CR and TA2CR to generate the watermarked time-domainaudio blocks TA1CW and TA2CW.

Based on the watermarked time-domain audio blocks 850, the modificationunit 430 may generate the watermarked MDCT coefficient sets 860. Forexample, the modification unit 430 may concatenate the watermarkedtime-domain audio blocks TA1CW and TA2CW to generate the watermarkedMDCT coefficient set M1CW. The modification unit 430 modifies the MDCTcoefficient sets 820 based on a corresponding one of the watermarkedMDCT coefficient sets 860. For example, the modification unit 430 mayuse the watermarked MDCT coefficient set M1CW to modify the originalMDCT coefficient set M1C. The modification unit 430 may then repeat theprocess described above for the audio blocks associated with eachchannel to insert the watermark 230 into the compressed digital datastream 800.

FIG. 9 is a flow diagram depicting one manner in which the examplewatermark embedding system of FIG. 2 may be configured to embed orinsert watermarks in a compressed digital data stream. The exampleprocess of FIG. 9 may be implemented as machine accessible instructionsutilizing any of many different programming codes stored on anycombination of machine-accessible media such as a volatile ornonvolatile memory or other mass storage device (e.g., a floppy disk, aCD, and a DVD). For example, the machine accessible instructions may beembodied in a machine-accessible medium such as a programmable gatearray, an application specific integrated circuit (ASIC), an erasableprogrammable read only memory (EPROM), a read only memory (ROM), arandom access memory (RAM), a magnetic media, an optical media, and/orany other suitable type of medium. Further, although a particular orderof actions is illustrated in FIG. 9, these actions can be performed inother temporal sequences. Again, the flow diagram 900 is merely providedand described in connection with the components of FIGS. 2 to 5 as anexample of one way to configure a system to embed watermarks in acompressed digital data stream.

In the example of FIG. 9, the process begins with the identifying unit410 (FIG. 4) identifying a frame associated with the compressed digitaldata stream 240 (FIG. 2) such as Frame A (FIG. 5) (block 910). Theidentified frame may include a plurality of MDCT coefficient sets formedby overlapping and concatenating a plurality of audio blocks. Inaccordance with the AC-3 compression standard, for example, a frame mayinclude six MDCT coefficient sets (i.e., six “audblk”). Further, theidentifying unit 410 (FIG. 4) also identifies header informationassociated with the frame (block 920). For example, the identifying unit410 may identify the number of channels associated with the compresseddigital data stream 240.

The unpacking unit 420 then unpacks the plurality of MDCT coefficientsets to determine compression information associated with the originalcompression process used to generate the compressed digital data stream240 (block 930). In particular, the unpacking unit 420 identifies themantissa M_(k) and the exponent X_(k) of each MDCT coefficient m_(k) ofeach of the MDCT coefficient sets. The exponents of the MDCTcoefficients may then be grouped in a manner compliant with the AC-3compression standard. The unpacking unit 420 (FIG. 4) also determinesthe number of bits used to represent the mantissa of each of the MDCTcoefficients so that a suitable quantization look-up table specified bythe AC-3 compression standard may be used to modify or augment theplurality of MDCT coefficient sets as described above in connection withFIG. 6. Control then proceeds to block 940 which is described in greaterdetail below in connection with FIG. 10.

As illustrated in FIG. 10, the modification process 940 begins by usingthe modifying unit 430 (FIG. 4) to perform an inverse transform of theMDCT coefficient sets to generate inverse transformed time-domain audioblocks (block 1010). In particular, the modification unit 430 generatesa previous (old) time-domain audio block (which, for example, isrepresented as a prime block in FIG. 5) and a current (new) time-domainaudio block (which is represented as a double-prime block in FIG. 5)associated with each of the 256-sample original time-domain audio blocksused to generate the corresponding MDCT coefficient set. As described inconnection with FIG. 5, for example, the modification unit 430 maygenerate TA4″ and TA5′ from the MDCT coefficient set MA5, TA5″ and TB0′from the MDCT coefficient set MB0, and TB0″ and TB1′ from the MDCTcoefficient set MB1. For each time-domain audio block, the modificationunit 430 adds corresponding prime and double-prime blocks to reconstructthe time-domain audio block based on, for example, the Princen-BradleyTDAC technique (block 1020). Following the above example, the primeblock TA5′ and the double-prime block TA5″ may be added to reconstructthe time-domain audio block TA5 (i.e., the reconstructed time-domainaudio block TA5R) while the prime block TB0′ and the double-prime blockTB0″ may be added to reconstruct the time-domain audio block TB0 (i.e.,the reconstructed time-domain audio block TB0R).

To insert the watermark 230, the modification unit 430 generatesmodifiable time-domain audio blocks using the reconstructed time-domainaudio blocks (block 1030). The modification unit 430 generates amodifiable 512-sample time-domain audio block using two adjacentreconstructed time-domain audio blocks. For example, the modificationunit 430 may generate a modifiable time-domain audio block byconcatenating the reconstructed time-domain audio blocks TA5R and TB0Rof FIG. 5.

Implementing an encoding process such as, for example, one or more ofthe encoding methods and apparatus described in U.S. Pat. Nos.6,272,176, 6,504,870, and/or 6,621,881, the modification unit 430inserts the watermark 230 from the watermark source 220 into themodifiable time-domain audio blocks (block 1040). For example, themodification unit 430 may insert the watermark 230 into the 512-sampletime-domain audio block generated using the reconstructed time-domainaudio blocks TA5R and TB0R to generate the watermarked time-domain audioblocks TA5W and TB0W. Based on the watermarked time-domain audio blocksand the compression information, the modification unit 430 generateswatermarked MDCT coefficient sets (block 1050). As noted above, twowatermarked time-domain audio blocks, where each block includes 256samples, may be used to generate a watermarked MDCT coefficient set. Forexample, the watermarked time-domain audio blocks TA5W and TBOW may beconcatenated and then used to generate the watermarked MDCT coefficientset MA5W.

Based on the compression information associated with the compresseddigital data stream 240, the modification unit 430 calculates themantissa value associated with each of the watermarked MDCT coefficientsin the watermarked MDCT coefficient set MA5W as described above inconnection with FIG. 6. In this manner, the modification unit 430 canmodify or augment the original MDCT coefficient sets using thewatermarked MDCT coefficient sets to embed or insert the watermark 230in the compressed digital data stream 240 (block 1060). Following theabove example, the modification unit 430 may replace the original MDCTcoefficient set MA5 based on the watermarked MDCT coefficient set MA5Wof FIG. 5. For example, the modification unit 430 may replace anoriginal MDCT coefficient in the MDCT coefficient set MA5 with acorresponding watermarked MDCT coefficient (which has an augmentedmantissa value) from the watermarked MDCT coefficient set MA5W.Alternatively, the modification unit 430 may compute the differencebetween the mantissa codes associated with the original MDCT coefficientand the corresponding watermarked MDCT coefficient (i.e.,ΔM_(k)=M_(k)−WM_(k)) and modify the original MDCT coefficient based onthe difference ΔM_(k). In either case, after modifying the original MDCTcoefficient sets, the modification process 940 terminates and returnscontrol to block 950.

Referring back to FIG. 9, the repacking unit 440 repacks the frame ofthe compressed digital data stream (block 950). The repacking unit 440identifies the position of the MDCT coefficient sets within the frame sothat the modified MDCT coefficient sets may be substituted in thepositions of the original MDCT coefficient sets to rebuild the frame. Atblock 960, if the embedding device 210 determines that additional framesof the compressed digital data stream 240 need to be processed, thencontrol returns to block 910. If, instead, all frames of the compresseddigital data stream 240 have been processed, then the process 900terminates.

As noted above, known watermarking techniques typically decompress acompressed digital data stream into uncompressed time-domain samples,insert the watermark into the time-domain samples, and recompress thewatermarked time-domain samples into a watermarked compressed digitaldata stream. In contrast, the digital data stream 240 remains compressedduring the example unpacking, modifying, and repacking processesdescribed herein. As a result, the watermark 230 is embedded into thecompressed digital data stream 240 without additionaldecompression/compression cycles that may degrade the quality of thecontent in the compressed digital data stream 500.

To further illustrate the example modification process 940 of FIGS. 9and 10, FIG. 11 depicts one manner in which a data frame (e.g., an AC-3frame) may be processed. The example frame processing process 1100begins with the embedding device 210 reading the header information ofthe acquired frame (e.g., an AC-3 frame) (block 1110) and initializingan MDCT coefficient set count to zero (block 1120). In the case where anAC-3 frame is being processed, each AC-3 frame includes six MDCTcoefficient sets having compressed-domain data (e.g., MA0, MA1, MA2,MA3, MA4 and MA5 of FIG. 5, which are also known as “audblks” in theAC-3 standard). Accordingly, the embedding device 210 determines whetherthe MDCT coefficient set count is equal to six (block 1130). If the MDCTcoefficient set count is not yet equal to six, thereby indicating thatat least one more MDCT coefficient set requires processing the embeddingdevice 210 extracts the exponent (block 1140) and the mantissa (block1150) associated with an MDCT coefficient of the frame (e.g., theoriginal mantissa M_(k) described above in connection with FIG. 6). Theembedding device 210 computes a new mantissa associated with a codesymbol read at block 1220 (e.g., the new mantissa WM_(k) described abovein connection with FIG. 6) (block 1160) and modifies the originalmantissa associated with the frame based on the new mantissa (block1170). For example, the original mantissa may be modified based on thedifference between the new mantissa and the original mantissa (butlimited within the range associated with the bit representation of theoriginal mantissa). The embedding device 210 increments the MDCTcoefficient set count by one (block 1180) and control returns to block1130. Although the example process of FIG. 11 is described above toinclude six MDCT coefficient sets (e.g., the threshold of the MDCTcoefficient set count is six), a process utilizing more or fewer MDCTcoefficient sets could be used instead. At block 1130, if the MDCTcoefficient set count is equal to six, then all MDCT coefficient setshave been processed such that the watermark has been embedded and theembedding device 210 repacks the frame (block 1190).

As noted above, many methods are known to embed a watermarkimperceptible to the human ear (e.g., an inaudible code) in anuncompressed audio signal. For example, one known method is described inU.S. Pat. No. 6,421,445 to Jensen et al., the disclosure of which ishereby incorporated by reference herein in its entirety. In particular,as described by Jensen et al., a code signal (e.g., a watermark) mayinclude information at a combination of ten different frequencies, whichare detectable by a decoder using a Fourier spectral analysis of asequence of audio samples (e.g., a sequence of 12,288 audio samples asdescribed in detail below). For example, an audio signal may be sampledat a rate of 48 kilo-Hertz (kHz) to output an audio sequence of 12,288audio samples that may be processed (e.g., using a Fourier transform) toacquire a relatively high-resolution (e.g., 3.9 Hz) frequency domainrepresentation of the uncompressed audio signal. However, in accordancewith the encoding process of the method disclosed by Jensen et al., asinusoidal code signal having constant amplitude across an entiresequence of audio samples is unacceptable because the sinusoidal codesignal may be perceptible to the human ear. To satisfy the maskingenergy constraints (i.e., to ensure that the sinusoidal code signalinformation remains imperceptible), the sinusoidal code signal issynthesized across the entire sequence of 12,288 audio samples using amasking energy analysis which determines a local sinusoidal amplitudewithin each block of audio samples (e.g., wherein each block of audiosamples may include 512 audio samples). Thus, the local sinusoidalwaveforms may be coherent (in-phase) across the sequence of 12,288 audiosamples but have varying amplitudes based on the masking energyanalysis.

However, in contrast to the method disclosed by Jensen et al., themethods and apparatus described herein may be used to embed a watermarkor other code signal in a compressed audio signal in a manner such thata compressed digital data stream containing the compressed audio signalremains compressed during the unpacking, modifying, and repackingprocesses. FIG. 12 depicts one manner in which a watermark, such as thatdisclosed by Jensen et al., may be inserted in a compressed audiosignal. The example process 1200 begins with initializing a frame countto zero (block 1210). Eight frames (e.g., AC-3 frames) representing atotal of 12,288 audio samples of each audio channel may be processed toembed one or more code symbols (e.g., one or more of the symbols “0”,“1”, “S”, and “E” shown in FIG. 13 and described in Jensen, et al.) intothe audio signal. Although the compressed digital data stream isdescribed herein to include 12,288 audio samples, the compressed digitaldata stream may have more or less audio samples. The embedding device210 (FIG. 2) may read a watermark 230 from the watermark source 220 toinject one or more code symbols into the sequence of frames (block1220). The embedding device 210 may acquire one of the frames (block1230) and proceed to the frame processing operation 1100 described aboveto process the acquired frame. Accordingly, the example frame processingoperation 1100 terminates and control returns to block 1250 to incrementthe frame count by one. The embedding device 210 determines whether theframe count is eight (block 1260). If the frame count is not eight, theembedding device 210 returns to acquire another frame in the sequenceand repeat the example frame processing operation 1100 as describedabove in connection with FIG. 11 to process another frame. If, instead,the frame count is eight, the embedding device 210 returns to block 1210to reinitialize the frame count to zero and repeat the process 1200 toprocess another sequence of frames.

As noted above, a code signal (e.g., the watermark 230) may be embeddedor injected into the compressed digital data stream (e.g., an AC-3 datastream). As shown in the example table 1300 of FIG. 13 and described inJensen, et al., the code signal may include a combination of tensinusoidal components corresponding to frequency indices f₁ through f₁₀to represent one of four code symbols “0,” “1,” “S,” and “E.” Forexample, the code symbol “0” may represent a binary value of zero andthe code symbol “1” may represent a binary value of one. Further, thecode symbol “S” may represent the start of a message and the code symbol“E” may represent the end of a message. While only four code symbols areshown in FIG. 13, more or fewer code symbols could be used instead.Additionally, table 1300 lists the transform bins corresponding to thecenter frequencies about which the ten sinusoidal components for eachsymbol are located. For example, the 512-sample central frequencyindices (e.g., 10, 12, 14, 16, 18, 20, 22, 24, 26, and 28) areassociated with a low resolution frequency domain representation of thecompressed digital data stream and the 12,288-sample central frequencyindices (e.g., 240, 288, 336, 384, 432, 480, 528, 576, 624, and 672) areassociated with a high resolution frequency domain representation of thecompressed digital data stream.

As noted above, each code symbol may be formed using ten sinusoidalcomponents associated with the frequency indices f₁ through f₁₀ depictedin table 1300. For example, a code signal for injecting or embedding thecode symbol “0” includes ten sinusoidal components corresponding to thefrequency indices 237, 289, 339, 383, 429, 481, 531, 575, 621, and 673,respectively. Likewise, a code signal for injecting or embedding thecode symbol “1” includes ten sinusoidal components corresponding to thefrequency indices 239, 291, 337, 381, 431, 483, 529, 573, 623, and 675,respectively. As shown in the example table 1300, each of the frequencyindices f₁ through f₁₀ has a unique frequency value at or proximate toeach of the 12,288-sample central frequency indices.

Each of the ten sinusoidal components associated with the frequencyindices f₁ through f₁₀ may be synthesized in the time domain using themethods and apparatus described herein. For example, the code signal forinjecting or embedding the code symbol “0” may include sinusoids c₁(k),c₂(k), c₃(k), c₄(k), c₅(k), c₆(k), c₇(k), c₈(k), c₉(k), and c₁₀(k). Thefirst sinusoid c₁(k) may be synthesized in the time domain as a sequenceof samples as follows:

${c_{1}(k)} = {\cos \; \frac{2\pi*237k}{12288}}$

for k=0 through 12287. However, the sinusoid c₁(k) generated in thismanner would have a constant amplitude over the entire 12,288 samplewindow. Instead, to generate a sinusoid whose amplitude may be variedfrom audio block to audio block, the sample values in a 512-sample audioblock (e.g., a long AC-3 block) associated with the first sinusoid c₁(k)may be computed as follows:

${c_{1p}(m)} = {{w(m)}\cos \; \frac{2\pi*237*\left( {{p*256} + m} \right)}{12288}}$

for m=0 through 511 and p=0 through 46, where w(m) is the windowfunction used in the AC-3 compression described above. One havingordinary skill in the art will appreciate that the preceding equationmay be used directly to compute c_(1p)(m), or c₁(k) may be pre-computedand appropriate segments extracted to generate c_(1p)(m). In eithercase, the MDCT transform of c_(1p) (m) includes a set of MDCTcoefficient values (e.g., 256 real numbers). Continuing with thepreceding example, for c_(1p)(m) corresponding to symbol “0,” the MDCTcoefficient values associated with the 512-sample frequency indices 9,10, and 11 may have significant magnitudes because c_(1p)(m) isassociated with the 12,288-sample central frequency index 240, whichcorresponds to the 512-sample central frequency index 10. The MDCTcoefficient values associated with other 512-sample frequency indiceswill be negligible relative to the MDCT coefficient values associatedwith the 512-sample frequency indices 9, 10, and 11 for the case ofc_(1p)(m). Conventionally, the MDCT coefficient values associated withc_(1p)(m) (as well as the other sinusoidal components c_(2p)(m), . . . ,c_(10p)(m)) are divided by a normalization factor Q as follows:

${Q = {\frac{512}{4} = 128}},$

where 512 is a number of samples associated with each block. Thisnormalization allows a time-domain cosine wave of unit amplitude at the12,288-sample central frequency index 240 to produce a unit amplitudeMDCT coefficient at the 512-sample central frequency index 10.

Continuing with the preceding example, for c_(1p)(m) associated withcode symbol “0,” the code frequency index 237 (e.g., the frequency valuecorresponding to the frequency index f₁ associated with the code symbol“0”) causes the 512-sample central frequency index 10 to have thehighest MDCT magnitude relative to the 512-sample frequency indices 9and 11 because the 512-sample central frequency index 10 corresponds tothe 12,288-sample central frequency index 240 and the code frequencyindex 237 is proximate to the 12,288-sample central frequency index 240.Likewise, the second frequency index f₂ corresponding to the codefrequency index 289 may produce MDCT coefficients with significant MDCTmagnitudes in the 512-sample frequency indices 11, 12, and 13. The codefrequency index 289 may cause the 512-sample central frequency index 12to have the highest MDCT magnitude because the 512-sample centralfrequency index 12 corresponds to the 12,288-sample central frequencyindex 288 and the code frequency index 289 is proximate to the12,288-sample central frequency index 288. Similarly, the thirdfrequency index f₃ corresponding to the code frequency index 339 mayproduce MDCT coefficients with significant MDCT magnitudes in the512-sample frequency indices 13, 14, and 15. The code frequency index339 may cause the 512-sample central frequency index 14 to have thehighest MDCT magnitude because the 512-sample central frequency index 14corresponds to the 12,288-sample central frequency index 336 and thecode frequency index 339 is proximate to the 12,288-sample centralfrequency index 336. Based on the sinusoidal components at each of theten frequency indices f₁ through f₁₀, the MDCT coefficients representingthe actual watermarked code signal will correspond to the 512-samplefrequency indices ranging from 9 to 29. Some of the 512-sample frequencyindices, such as, for example, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27,and 29 may be influenced by energy spill-over from two neighboring codefrequency indices, with the amount of spill-over a function of theweighting applied to each sinusoidal component based on the maskingenergy analysis. Accordingly, in each 512-sample audio block of thecompressed digital data stream, the MDCT coefficients may be computed asdescribed below to represent the code signal.

In the compressed AC-3 data stream, for example, each AC-3 frameincludes MDCT coefficient sets having six MDCT coefficients (e.g., MA0,MA1, MA2, MA3, MA4, and MA5 of FIG. 5) with each MDCT coefficientcorresponding to a 512-sample audio block. As described above inconnection with FIGS. 5 and 6, each MDCT coefficient is represented asm_(k)=M_(k)*2^(−X) ^(k) =(S_(k)*N_(k))*2^(−X) ^(k) , where X_(k) is theexponent and M_(k) is the mantissa. The mantissa M_(k) is a product of amantissa step size s_(k) and an integer value N_(k). The mantissa stepsize s_(k) and the exponent X_(k) may be used to form a quantizationstep size S_(k)=S_(k)*2^(−X) ^(k) . Referring to the look-up table 600of FIG. 6, for example, the mantissa step size s_(k) is 2/15 and theinteger value N_(k) is −2 when the original mantissa value is −0.2666(i.e., − 4/15).

To inject a code signal into the compressed AC-3 data stream,modifications to the mantissa set M_(k) for k=9 through 29 aredetermined. For example, consider a subset of the mantissa set M_(k) fork=9 through 29 in which the MDCT coefficient magnitudes C₉, C₁₀, and C₁₁corresponding to the watermarked MDCT coefficients wm₉, wm₁₀, and wm₁₁are −0.3, 0.8, and 0.2, respectively (with the varying amplitude basedon the local masking energy). Furthermore, assume that the code MDCTmagnitude C₁₁ associated with the 512-sample central frequency index 11is the MDCT coefficient having the lowest absolute magnitude (e.g., anabsolute value of 0.2) for the entire mantissa set (C_(k) for k=9through 29). The value of the code MDCT magnitude C₁₁ is used tonormalize and modify the values of the MDCT coefficients m₉, m₁₀, andm₁₁ (as well as the other MDCT coefficients in the set m₉ through m₂₉)because the code MDCT magnitude C₁₁ has the lowest absolute magnitude.First, C₁₁ is normalized to 1.0 and then used to normalize, for example,C₉ and C₁₀ as C₉=−0.3/C₁₁=−1.5 and C₁₀=0.8/C₁₁=4.0. Then, the mantissainteger value N₁₁ corresponding to the original MDCT coefficient m₁₁ isincreased by 1 to as this is the minimum amount (due to mantissa stepsize quantization) by which m₁₁ may be modified to reflect the additionof the watermark code corresponding to C₁₁. Finally, the mantissainteger values N₉ and N₁₀ corresponding to the original MDCTcoefficients m₉ and m₁₀ are modified relative to N₁₁ as follows:

$N_{9}->{{N_{9} + {\frac{{- 1.5}*S_{11}}{S_{9}}\mspace{14mu} {and}\mspace{14mu} N_{10}}}->{N_{10} + {\frac{4.0*S_{11}}{S_{10}}.}}}$

Thus, the modified mantissa integer values N₉, N₁₀, and N₁₁ (and thesimilarly modified mantissa integers N₁₂ through N₂₉) may be used tomodify the corresponding original MDCT coefficients to embed thewatermark code. Also, as mentioned previously, for any MDCT coefficient,the maximum change is limited by the upper and lower limits of itsmantissa integer value N_(k). Referring to FIG. 6, for example, thetable 600 indicates lower limit and upper limit values of −0.9333 to+0.9333.

Thus, the preceding example illustrates how the local masking energy maybe used to determine the code magnitude for code symbols to be embeddedinto a compressed audio signal digital data stream. Moreover, eightsuccessive frames of the compressed digital data stream were modifiedwithout performing decompression of MDCT coefficients during theencoding process of the methods and apparatus described herein.

FIG. 14 is a block diagram of an example processor system 2000 that mayused to implement the methods and apparatus disclosed herein. Theprocessor system 2000 may be a desktop computer, a laptop computer, anotebook computer, a personal digital assistant (PDA), a server, anInternet appliance or any other type of computing device.

The processor system 2000 illustrated in FIG. 14 includes a chipset2010, which includes a memory controller 2012 and an input/output (I/O)controller 2014. As is well known, a chipset typically provides memoryand I/O management functions, as well as a plurality of general purposeand/or special purpose registers, timers, etc. that are accessible orused by a processor 2020. The processor 2020 is implemented using one ormore processors. In the alternative, other processing technology may beused to implement the processor 2020. The processor 2020 includes acache 2022, which may be implemented using a first-level unified cache(L1), a second-level unified cache (L2), a third-level unified cache(L3), and/or any other suitable structures to store data.

As is conventional, the memory controller 2012 performs functions thatenable the processor 2020 to access and communicate with a main memory2030 including a volatile memory 2032 and a non-volatile memory 2034 viaa bus 2040. The volatile memory 2032 may be implemented by SynchronousDynamic Random Access Memory (SDRAM), Dynamic Random Access Memory(DRAM), RAMBUS Dynamic Random Access Memory (RDRAM), and/or any othertype of random access memory device. The non-volatile memory 2034 may beimplemented using flash memory, Read Only Memory (ROM), ElectricallyErasable Programmable Read Only Memory (EEPROM), and/or any otherdesired type of memory device.

The processor system 2000 also includes an interface circuit 2050 thatis coupled to the bus 2040. The interface circuit 2050 may beimplemented using any type of well known interface standard such as anEthernet interface, a universal serial bus (USB), a third generationinput/output interface (3GIO) interface, and/or any other suitable typeof interface.

One or more input devices 2060 are connected to the interface circuit2050. The input device(s) 2060 permit a user to enter data and commandsinto the processor 2020. For example, the input device(s) 2060 may beimplemented by a keyboard, a mouse, a touch-sensitive display, a trackpad, a track ball, an isopoint, and/or a voice recognition system.

One or more output devices 2070 are also connected to the interfacecircuit 2050. For example, the output device(s) 2070 may be implementedby media presentation devices (e.g., a light emitting display (LED), aliquid crystal display (LCD), a cathode ray tube (CRT) display, aprinter and/or speakers). The interface circuit 2050, thus, typicallyincludes, among other things, a graphics driver card.

The processor system 2000 also includes one or more mass storage devices2080 to store software and data. Examples of such mass storage device(s)2080 include floppy disks and drives, hard disk drives, compact disksand drives, and digital versatile disks (DVD) and drives.

The interface circuit 2050 also includes a communication device such asa modem or a network interface card to facilitate exchange of data withexternal computers via a network. The communication link between theprocessor system 2000 and the network may be any type of networkconnection such as an Ethernet connection, a digital subscriber line(DSL), a telephone line, a cellular telephone system, a coaxial cable,etc.

Access to the input device(s) 2060, the output device(s) 2070, the massstorage device(s) 2080 and/or the network is typically controlled by theI/O controller 2014 in a conventional manner. In particular, the I/Ocontroller 2014 performs functions that enable the processor 2020 tocommunicate with the input device(s) 2060, the output device(s) 2070,the mass storage device(s) 2080 and/or the network via the bus 2040 andthe interface circuit 2050.

While the components shown in FIG. 14 are depicted as separate blockswithin the processor system 2000, the functions performed by some ofthese blocks may be integrated within a single semiconductor circuit ormay be implemented using two or more separate integrated circuits. Forexample, although the memory controller 2012 and the I/O controller 2014are depicted as separate blocks within the chipset 2010, the memorycontroller 2012 and the I/O controller 2014 may be integrated within asingle semiconductor circuit.

The methods and apparatus disclosed herein are particularly well suitedfor use with data streams implemented in accordance with the AC-3standard. However, the methods and apparatus disclosed herein may beapplied to other digital audio coding techniques.

In addition, while this disclosure is made with respect to exampletelevision systems, it should be understood that the disclosed system isreadily applicable to many other media systems. Accordingly, while thisdisclosure describes example systems and processes, the disclosedexamples are not the only way to implement such systems.

Although certain example methods, apparatus, and articles of manufacturehave been described herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus, and articles of manufacture fairly falling within the scopeof the appended claims either literally or under the doctrine ofequivalents. For example, although this disclosure describes examplesystems including, among other components, software executed onhardware, it should be noted that such systems are merely illustrativeand should not be considered as limiting. In particular, it iscontemplated that any or all of the disclosed hardware and softwarecomponents could be embodied exclusively in dedicated hardware,exclusively in firmware, exclusively in software or in some combinationof hardware, firmware, and/or software.

What is claimed is:
 1. A method to embed a watermark in a compresseddata stream, the method comprising: obtaining a set of transformcoefficients included in the compressed data stream, the set oftransform coefficients comprising a first set of mantissa codes and aset of exponents, the first set of mantissa codes associated with arespective set of step sizes; identifying a first transform coefficientfrom the set of transform coefficients having a smallest magnitude amongthe set of transform coefficients; determining a second set of mantissacodes based on the first transform coefficient and the set of stepsizes; and replacing the first set of mantissa codes in the compresseddata stream with the second set of mantissa codes to embed the watermarkwithout uncompressing the compressed data stream.